Molding die for molding boot for constant velocity joint

ABSTRACT

An inner die of a molding die includes a core shaft, split dies radially arranged along an outer peripheral surface of the core shaft around an axis of the core shaft, which serves as a center, and a cylindrical set ring arranged below the split dies, the core shaft being inserted through the set ring. An annular engaging surface, which is a tapered surface whose diameter is gradually reduced downward, is formed in an inner peripheral side of an upper end portion of the set ring, and lower end portions of the respective split dies are introduced into, and engaged with the engaging surface. The molding die includes a pressing portion that presses downward upper end portions of the respective split dies introduced into the set ring, so as to move the lower end portions of the respective split dies toward the axis along the engaging surface.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2012-257532 filed onNov. 26, 2012 including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a molding die for molding a boot for aconstant velocity joint.

2. Description of Related Art

For example, in vehicles such as an automobile, constant velocity jointsare used in order to transmit a rotation force to driving wheels thatmove upward and downward according to a road surface. A boot for aconstant velocity joint made of synthetic resin is fitted to theconstant velocity joint, in order to protect the constant velocity jointfrom external muddy water or dust and to retain lubricating greasesupplied to the constant velocity joint. The boot for a constantvelocity joint includes a cylindrical larger-diameter portion and acylindrical smaller-diameter portion, and a bellows portion connectingthe larger-diameter portion and the smaller-diameter portion. The bootfor a constant velocity joint is generally formed by a blow moldingmethod.

In the above-described blow molding method, molding is performed bysetting molten resin formed in the shape of a bag, within an outer die,and by expanding the bag-shaped molten resin using a blow of air so thatthe molten resin is pressed against the outer die, without using aninner die. Thus, in the blow molding method, an inner peripheral surfaceof the boot for a constant velocity joint cannot be molded with highprecision. Therefore, it cannot be said that the blow molding method isoptimal as the method of molding the boot for a constant velocity joint,which requires a precise bellows structure. Thus, as shown in JapanesePatent Application Publication No. 2012-126033 (JP 2012-126033 A), amethod of molding a boot for a constant velocity joint by injectionmolding with use of an outer die and an inner die (core die) issuggested.

The inner die used for the injection molding in JP 2012-126033 A isconstituted by a center core formed so that the diameter thereof isgradually increased from an upper end toward a lower end, and aplurality of split dies arranged along an outer periphery of the centercore. This inner die is again assembled after the center core and thesplit dies are separated in order to take out a compact from the outerdie when the molding of the boot for a constant velocity joint iscompleted.

However, in the inner die described in JP 2012-126033 A, a process ofpushing up the center core to push the split dies radially outward (theprocess of changing the state from the state shown in FIG. 3 to thestate shown in FIG. 1 in JP 2012-126033 A) is required when the centercore and the split dies are fitted to each other. Therefore, when thecenter core is pushed up, a gap is likely to be formed between the splitdies adjacent to each other in the circumferential direction. Ifinjection molding is performed in a state where this gap is formed,burrs are generated in the compact.

SUMMARY OF THE INVENTION

An object of the invention is to provide a molding die for molding aboot for a constant velocity joint, which can prevent burrs from beinggenerated in a compact molded by injection molding.

According to an aspect of the invention, there is provided a molding diefor molding a boot for a constant velocity joint by injection molding,the molding die including an inner die and an outer die arranged so thata cavity is formed between the inner die and the outer die, the moldingdie being characterized in that: the inner die includes a core shafthaving a circular outer peripheral surface and being arranged so that anaxis of the core shaft extends in an up-down direction, a plurality ofsplit dies radially arranged along the outer peripheral surface of thecore shaft around the axis of the core shaft, which serves as a center,and a cylindrical set ring arranged below the split dies, the core shaftbeing inserted through the set ring; an annular engaging surface, whichis a tapered surface whose diameter is gradually reduced downward, isformed in an inner peripheral side of an upper end portion of the setring, and lower end portions of the respective split dies are introducedinto, and engaged with the engaging surface; and the molding dieincludes a pressing portion that presses upper end portions of therespective split dies downward in a state where the lower end portionsof the respective split dies are introduced into the set ring, so as toengage the lower end portions of the respective split dies with theengaging surface and to bring the split dies into close contact witheach other.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further features and advantages of the invention willbecome apparent from the following description of example embodimentswith reference to the accompanying drawings, wherein like numerals areused to represent like elements and wherein:

FIG. 1 is a sectional view showing a molding die used in a method ofmolding a boot for a constant velocity joint according to an embodimentof the invention;

FIG. 2 is a schematic plan view showing an inner die in the molding die;

FIG. 3 is a sectional view showing a state where the inner die isremoved from a lower die in the molding die;

FIG. 4 is a sectional view showing a disassembling-assembling machinethat disassembles and assembles the inner die;

FIG. 5 is a sectional view showing the operating state of supportingmembers of the disassembling-assembling machine;

FIG. 6 is a plan view showing the supporting members;

FIG. 7 is a sectional view showing the operating state of first clampsof the disassembling-assembling machine;

FIG. 8 is a sectional view showing the operating state of an ejector andsecond clamps of the disassembling-assembling machine;

FIGS. 9A and 9B are sectional views showing the disassembling-assemblingmachine while processes of the molding method are performed;

FIGS. 10A and 10B are sectional views showing thedisassembling-assembling machine while processes of the molding methodare performed;

FIGS. 11A and 11B are sectional views showing thedisassembling-assembling machine while processes of the molding methodare performed; and

FIGS. 12A to 12D are plan views showing a procedure of separating splitdies from each other by the disassembling-assembling machine.

DETAILED DESCRIPTION OF EMBODIMENTS

Next, preferable embodiments of the invention will be described withreference to the accompanying drawings. FIG. 1 is a sectional viewshowing a molding die used in a method of molding a boot for a constantvelocity joint according to an embodiment of the invention. In FIG. 1, amolding die 1 is used for molding a boot 9 for a constant velocity jointby injection molding. The molding die 1 is constituted by a pair ofright and left outer dies 11, an inner die 12, and a lower die 13. Theinner die 12 is arranged inside the outer dies 11. The lower die 13 isarranged under the outer dies 11. The boot 9 for a constant velocityjoint is constituted by a larger-diameter portion 9 a and asmaller-diameter portion 9 c that are formed in a cylindrical shape, anda bellows portion 9 b. The bellows portion 9 b connects thelarger-diameter portion 9 a and the smaller-diameter portion 9 c.

The outer dies 11 are arranged on an upper surface of the lower die 13to be movable in a horizontal direction (right-and-left direction ofFIG. 1). In internal surfaces of the outer dies 11, die surfaces 11 aare formed. The die surfaces 11 a correspond to the shapes of respectiveouter peripheral surfaces of the larger-diameter portion 9 a, thebellows portion 9 b, and the smaller-diameter portion 9 c in the boot 9for a constant velocity joint. A cavity 19 b is formed between the diesurfaces 11 a and die surfaces 152 a to 152 h (to be described below) ofthe inner die 12. In the outer dies 11, an introduction path 11 b isformed to introduce a molding material into the cavity 19 b or the like.As the molding material, for example, an elastomer (a thermoplasticpolyester elastomer, a thermoplastic polyolefin-based elastomer, or thelike) is used.

On the upper surface of the lower die 13, a stepped portion 13 a thatprotrudes upward is formed, and a fitting hole 13 b is formed in thestepped portion 13 a. In a side surface of the stepped portion 13 a, adie surface 13 c is formed. The die surface 13 c corresponds to theshape of an inner peripheral surface of the larger-diameter portion 9 ain the boot 9 for a constant velocity joint. A cavity 19 c is formedbetween the die surface 13 c and the die surfaces 11 a of the outer dies11. The inner die 12 is constituted by a core shaft 14, a plurality ofsplit dies 15 a to 15 h (refer to FIG. 2), and a set ring 16. The coreshaft 14 is arranged so that an X axis extends in an up-down direction.The split dies 15 a to 15 h are arranged radially outside the core shaft14. The set ring 16 is arranged below the split dies 15 a to 15 h.

The core shaft 14 is made of a solid columnar member, and has a circularouter peripheral surface 14 a. An annular protruding portion 14 b (apressing portion) that protrudes radially outward is formed integrallywith an outer periphery of an upper end portion of the core shaft 14. Alower surface of the protruding portion 14 b abuts on upper surfaces ofthe respective split dies 15 a to 15 h so as to press upper end portionsof the respective split dies 15 a to 15 h downward (also refer to FIG.2).

In an outer peripheral surface of the protruding portion 14 b, a diesurface 14 c is formed. The die surface 14 c corresponds to the shape ofan inner peripheral surface of the smaller-diameter portion 9 c in theboot 9 for a constant velocity joint. A cavity 19 a is formed betweenthe die surface 14 c and the die surfaces 11 a of the outer dies 11. Aplurality of recessed engagement portions 14 d is formed integrally withan outer periphery of a lower end portion of the core shaft 14. Apulling device 10 that pulls the lower end portion of the core shaft 14downward is engaged with the engagement portions 14 d. The pullingdevice 10 has a plurality of hook portions 10 a, each of which can beengaged with a corresponding one of the engagement portions 14 d.

FIG. 2 is a schematic plan view showing the inner die 12. In FIGS. 1 and2, the inner die 12 includes the first to fourth split dies 15 a to 15d, and the fifth to eighth split dies 15 e to 15 h as the split dies 15a to 15 h. Each of the split dies 15 a to 15 d is formed in arectangular shape in the plan view. Each of the split dies 15 e to 15 his formed in a fan shape in the plan view. The split dies 15 a to 15 hare radially arranged along the outer peripheral surface 14 a of thecore shaft 14 around the X axis of the core shaft 14, which serves as acenter. In that case, the split dies 15 a to 15 d that are rectangularin the plan view and the split dies 15 e to 15 h that are fan-shaped inthe plan view are alternately arranged in the circumferential direction,and are formed in a circular shape in the plan view as a whole.

In FIGS. 1 and 2, each of inner peripheral surfaces 151 a to 151 h ofthe split dies 15 a to 15 h is formed in the shape of a circular arcalong the outer peripheral surface 14 a of the core shaft 14. In outerperipheral surfaces of the split dies 15 a to 15 h, the die surfaces 152a to 152 h are formed so as to correspond to the shapes of therespective inner peripheral surfaces of the larger-diameter portion 9 aand the bellows portion 9 b in the boot 9 for a constant velocity joint.Lower surfaces of the respective split dies 15 a to 15 h are placed onthe stepped portion 13 a of the lower die 13.

In the lower surfaces of the respective split dies 15 a to 15 h, firstrecessed portions 153 a to 153 h and second recessed portions 154 a to154 h, each of which has a quadrangular section, are formed. An upperend portion of the set ring 16 is inserted into the first recessedportions 153 a to 153 h. First to eighth supporting member 23 a to 23 hto be described below are inserted into the second recessed portions 154a to 154 h, respectively. The first recessed portions 153 a to 153 h areannularly formed as a whole in a state where the split dies 15 a to 15 hare arranged in a circular shape in the plan view as shown in FIG. 2. Inthis state, in internal surfaces of the first recessed portions 153 a to153 h, an annular engaged surface 15 i is formed. The annular engagedsurface 15 i is a tapered surface whose diameter is gradually reduceddownward from an upper end. External surfaces of the first recessedportions 153 a to 153 h are formed so as to face the outer peripheralsurface of the set ring 16 in a state where the upper end portion of theset ring 16 is inserted into the first recessed portions 153 a to 153 h.

In FIG. 1, the set ring 16 is formed in a cylindrical shape as a wholeand is detachably fitted in the fitting hole 13 b of the lower die 13. Alower portion of the core shaft 14 is inserted through an innerperipheral surface 16 a of the set ring 16 so as to be movable in theup-down direction. In an inner peripheral side of the upper end portionof the set ring 16, an annular engaging surface 16 b is formed. Lowerend portions of the respective split dies 15 a to 15 h are introducedinto, and engaged with the engaging surface 16 b in a state where theupper end portion of the set ring 16 is inserted into the first recessedportions 153 a to 153 h. The engaging surface 16 b is formed to have alarger diameter than the inner peripheral surface 16 a, and isconstituted by a tapered surface whose diameter is gradually reduceddownward from an upper end.

In an outer periphery of the upper end portion of the set ring 16, anannular groove 16 c is formed. An O ring 17 is fitted in the annulargroove 16 c. The O ring 17 comes into pressure contact with the externalsurfaces (opposed surfaces) of the first recessed portions 153 a to 153h of the respective split dies 15 a to 15 h. A plurality of firstengaging grooves 16 d is formed under the annular groove 16 c at anouter periphery of the set ring 16. A plurality of lug portions 3 a(refer to FIG. 3) of a chuck 3 is engaged with the first engaginggrooves 16 d, respectively. In an outer periphery of a lower end portionof the set ring 16, a plurality of second engaging grooves 16 e isformed. Engaging lugs 22 c of holding members 22 to be described beloware engaged with the second engaging grooves 16 e, respectively.

FIG. 3 is a sectional view showing a state where the inner die 12 isremoved from the lower die 13 after injection molding. In FIG. 3, aplurality of (for example, four) ejectors 18, each of which is formed ina rod shape, is arranged at the lower die 13 so as to be movable upwardand downward, in order to push up a lower surface of the set ring 16fitted in the fitting hole 13 b. Thus, the lower surface of the set ring16 can be pushed up by moving the ejectors 18 upward as shown in FIG. 3after the paired outer dies 11 in the state shown in FIG. 1 are moved toright and left sides, respectively, so as to be separated from the innerdie 12. When the set ring 16 is pushed up in this way, the core shaft14, the split dies 15 a to 15 h, and a compact W of the boot 9 for aconstant velocity joint are moved upward together with the set ring 16,and the inner die 12 can be separated above the lower die 13. Further,from this state, the lug portions 3 a of the chuck 3 are engaged withthe respective engaging grooves 16 d of the set ring 16 and the lugportions 3 a are raised so that the inner die 12 and the compact W canbe moved to a disassembling-assembling machine 2 to be described below.

FIG. 4 is a sectional view showing the disassembling-assembling machinethat disassembles and assembles the inner die 12. In FIG. 4, thedisassembling-assembling machine 2 disassembles the inner die 12 movedfrom the molding die 1 by the chuck 3 to take out the compact W, andassembles the disassembled inner die 12 again. Thedisassembling-assembling machine 2 includes a base 21, the pairedholding members 22, the first to eighth supporting members 23 a to 23 h(refer to FIG. 6), paired first clamps 24 (refer to FIG. 7), an ejector25 (refer to FIG. 8), and paired second clamps 26 (refer to FIG. 8).

In FIG. 4, the base 21 has a cylindrical portion 21 a that supports thecore shaft 14 in a state where the X axis of the core shaft 14 extendsin the up-down direction and the end portion of the core shaft 14 isinserted in the cylindrical portion 21 a. An upper surface of thecylindrical portion 21 a restricts the downward movement of the coreshaft 14 by abutting on the lower surface of the set ring 16 when thelower end portion of the core shaft 14 is inserted in the cylindricalportion 21 a. In a bottom of the cylindrical portion 21 a, a throughhole 21 b is formed. The ejector 25 is inserted through the through hole21 b from below the base 21.

The paired holding members 22 hold the set ring 16 in a state where theset ring 16 is arranged on the cylindrical portion 21 a of the base 21.The holding members 22 are arranged above the base 21 so as to bemovable in the horizontal direction (right-and-left direction in FIG.4). A distal end portion of each holding member 22 is formed to have anL-shape section constituted by a horizontal portion 22 a and a verticalportion 22 b. In an upper end portion of the vertical portion 22 b, theengaging lug 22 c is formed and is engaged with the corresponding secondengaging groove 16 e of the set ring 16. The disassembling-assemblingmachine 2 further includes a cutting device (not shown) that cuts arunner portion 4 (cross-hatched portion in FIG. 4) molded in theintroduction path 11 b of the outer dies 11, in the state shown in FIG.4.

FIG. 5 is a sectional view showing the operating state of the first toeighth supporting members 23 a to 23 h of the disassembling-assemblingmachine 2. In FIGS. 4 and 5, the first to eighth supporting members 23 ato 23 h support the respective split dies 15 a to 15 h in a state wherethe split dies 15 a to 15 h are separated from the set ring 16. Thesupporting members 23 a to 23 h are arranged between the horizontalportions 22 a of the holding members 22 and the split dies 15 a to 15 hand are individually movable in the up-down direction and the horizontaldirection. The supporting members 23 a to 23 h have rod-shaped engagingportions 231 a to 231 h that are located at the distal end portions ofthe respective supporting members 23 a to 23 h, and that extend in theup-down direction. The engaging portions 231 a to 231 h are respectivelyengaged with the second recessed portions 154 a to 154 h of the splitdies 15 a to 15 h.

FIG. 6 is a plan view showing the first to eighth supporting members 23a to 23 h. As shown in FIG. 6, the first to eighth supporting members 23a to 23 h are radially arranged around the X axis that serves as thecenter. Each of the engaging portions 231 a to 231 h of the supportingmembers 23 a to 23 h is formed to have a quadrangular section inaccordance with the sectional shape of each of the second recessedportions 154 a to 154 h of the split dies 15 a to 15 h. As a result, itis possible to restrict the split dies 15 a to 15 h, which are supportedby the supporting members 23 a to 23 h, from being rotated in thehorizontal direction around the supporting members 23 a to 23 h.

FIG. 7 is a sectional view showing the operating state of the firstclamps 24 of the disassembling-assembling machine 2. In FIG. 7, thepaired first clamps 24 hold the compact W when the split dies 15 a to 15h are raised by the supporting members 23 a to 23 h. The first clamps 24are arranged so as to be movable in the horizontal direction(right-and-left direction in the drawing) and in the up-down direction.In an internal surface of each first clamp 24, a holding surface 24 a isformed so as to correspond to the shapes of the respective outerperipheral surfaces of the larger-diameter portion 9 a, the bellowsportion 9 b, and the smaller-diameter portion 9 c in the compact W. Thecompact W can be held by the holding surfaces 24 a in a state where theouter peripheral surface of the compact W is sandwiched between theholding surfaces 24 a on the right and left sides.

FIG. 8 is a sectional view showing the operating state of the ejector 25and the second clamps 26 of the disassembling-assembling machine 2. InFIG. 8, the ejector 25 pushes up the lower surface of the core shaft 14inserted into the cylindrical portion 21 a of the base 21, and isconstituted by a rod-shaped member that can be inserted through thethrough hole 21 b of the base 21 from below the base 21. The pairedsecond clamps 26 hold and pull out upward the upper end portion of thecore shaft 14 pushed up by the ejector 25, and are arranged above thefirst clamps 24 so as to be movable upward and downward. In a distal endportion of each second clamp 26, an engaging portion 26 a is formed. Theengaging portion 26 a is engaged with an upper end corner portion of theprotruding portion 14 b of the core shaft 14. The core shaft 14 can beheld by the engaging portions 26 a in a state where the upper endportion of the core shaft 14 is sandwiched between the engaging portions26 a on the right and left sides.

Next, a method of molding the boot 9 for a constant velocity joint usingthe molding die 1 and the disassembling-assembling machine 2 describedabove will be described. First, as shown in FIG. 1, in the molding die1, the lower end portion of the core shaft 14 is held in a state wherethe hook portions 10 a of the pulling device 10 are engaged with theengagement portions 14 d of the lower end portion of the core shaft 14,and the lower end portion of the core shaft 14 is pulled downward. Atthis time, the protruding portion 14 b of the upper end portion of thecore shaft 14 presses the split dies 15 a to 15 h of the inner die 12downward, and therefore, the lower end portions of the split dies 15 ato 15 h are moved toward the X axis along the engaging surface 16 b thatis the tapered surface of the set ring 16, and are engaged with theengaging surface 16 b. Thus, the split dies 15 a to 15 h adjacent toeach other in the circumferential direction can be held in a state wherethe split dies 15 a to 15 h are in close contact with each other.

Next, the compact W of the boot 9 for a constant velocity joint ismolded by injection molding with use of the paired outer dies 11, theinner die 12, and the lower die 13 in the molding die 1. Specifically,the compact W is molded by injection molding by introducing a moldingmaterial into the cavities 19 a to 19 c sequentially from theintroduction path 11 b of the outer dies 11. In that case, in theintroduction path 11 b, the runner portion 4 (refer to FIG. 3) is alsomolded integrally with the compact W. After the compact W is molded byinjection molding, the tool is removed from the engagement portions 14 dof the core shaft 14 and the downward pulling of the core shaft 14 isstopped.

Next, after the paired outer dies 11 are moved to the right and leftsides, respectively, from the state shown in FIG. 1 so as to beseparated from the inner die 12, the inner die 12 is separated from thelower die 13. Specifically, as shown in FIG. 3, the lower surface of theset ring 16 is pushed up by the ejectors 18, and the set ring 16 ismoved to above the lower die 13 together with the core shaft 14, thesplit dies 15 a to 15 h, and the compact W. From this state, the setring 16 is raised by engaging the lug portions 3 a of the chuck 3 withthe respective engaging grooves 16 d of the set ring 16. Thus, the innerdie 12 can be separated from the lower die 13.

Next, the inner die 12 is moved to the disassembling-assembling machine2 together with the compact W by the chuck 3, and as shown in FIG. 4,the lower end portion of the core shaft 14 of the inner die 12 isinserted into the cylindrical portion 21 a of the base 21, and thepaired holding members 22 are engaged with the second engaging grooves16 e of the set ring 16. As a result, the set ring 16 is held on thebase 21. Then, in this state, the runner portion 4 molded integrallywith the compact W is cut.

Next, the first to eighth supporting members 23 a to 23 h are movedupward from the state shown in FIG. 4, and the engaging portions 231 ato 231 h thereof are engaged with the second recessed portions 154 a to154 h of the respective split dies 15 a to 15 h. From this state, thefirst to eighth supporting members 23 a to 23 h are further moved upwardto raise the respective split dies 15 a to 15 h. At this time, theentire inner die 12 is about to be raised. However, since the set ring16 is held on the base 21 by the holding member 22, the split dies 15 ato 15 h and the core shaft 14 move upward with respect to the set ring16 as shown in FIG. 5. Thus, the split dies 15 a to 15 h can beseparated from the set ring 16, together with the compact W.

Next, as shown in FIG. 7, the paired first clamps 24 are respectivelymoved in the directions indicated by arrows in the drawing, and hold thecompact W in a state where the compact W is sandwiched between the firstclamps 24 on the right and left sides. Then, as shown in FIG. 8, theejector 25 is inserted through the through hole 21 b of the base 21 frombelow the base 21, and thus, the lower surface of the core shaft 14 ispushed up. At this time, the set ring 16 is held by the holding members22, and the upward and downward movement of the split dies 15 a to 15 his restricted by the first clamps 24 via the compact W. Therefore, onlythe core shaft 14 moves upward. As a result, the upper end portion ofthe core shaft 14 protrudes upward from the first clamps 24.

Further, from this state, the core shaft 14 is held by the paired secondclamps 26 in a state where the upper end portion of the core shaft 14 issandwiched between the second clamps 26 on the right and left sides, andthe second clamps 26 are moved upward. Thus, the core shaft 14 can beseparated from the set ring 16 and the split dies 15 a to 15 h as shownin FIG. 9A. When the second clamps 26 are moved upward, the first clamps24 are also moved upward while the first clamps 24 hold the compact W.

FIGS. 9 to 11 are sectional views showing the disassembling-assemblingmachine 2 while processes of the molding method are performed. After thecore shaft 14, the set ring 16, and the split dies 15 a to 15 h areseparated from each other in the up-down direction as shown in FIG. 9A,the split dies 15 a to 15 h are separated from the compact W.Specifically, as shown in FIG. 9B, the split dies 15 a to 15 h arehorizontally shifted toward the center thereof, that is, toward the Xaxis by the respective supporting members 23 a to 23 h. At this time,the split dies 15 a to 15 h are moved to positions where the diesurfaces 152 a to 152 h of the respective split dies 15 a to 15 h do notinterfere with the bellows portion 9 b of the compact W. Then, as shownin FIG. 10A, by moving the supporting members 23 a to 23 h downward, thesplit dies 15 a to 15 h are pulled out downward and separated from thecompact W.

FIGS. 12A to 12D are plan views showing a detailed procedure ofseparating the split dies 15 a to 15 h from each other. First, among thesplit dies 15 a to 15 h formed in a circular shape in the plan view asshown in FIG. 12A, the first to fourth split dies 15 a to 15 d, each ofwhich has a rectangular shape in the plan view, are separated from thecompact W. Specifically, first, the first split die 15 a is horizontallyshifted toward the X axis and brought into a state shown in FIG. 12B.From this state, the first split die 15 a is pulled out downward andseparated from the compact W. By the same method as this, the thirdsplit die 15 c, the second split die 15 b, and the fourth split die 15 dare separated in this order from the compact W and brought into thestate shown in FIG. 12C.

Next, the remaining fifth to eighth split dies 15 e to 15 h, each ofwhich has a fan shape in the plan view, are separated from the compactW. Specifically, first, the fifth split die 15 e is horizontally shiftedtoward the X axis and brought into a state shown in FIG. 12D. From thisstate, the fifth split die 15 e is pulled out downward and separatedfrom the compact W. By the same method as this, the seventh split die 15g, the sixth split die 15 f, and the eighth split die 15 h are separatedin this order from the compact W.

As shown in FIG. 10A, each of the split dies 15 a to 15 h separated fromthe compact W is horizontally moved in a direction opposite to adirection in which the split die has been horizontally shifted by acorresponding one of the supporting members 23 a to 23 h, and is thenmoved downward. As a result, as shown in FIG. 10B, the lower endportions of the respective split dies 15 a to 15 h are introduced intothe inner peripheral side of the upper end portion of the set ring 16while the engaged surface 15 i of the split dies 15 a to 15 h movesalong the engaging surface 16 b of the set ring 16. The split dies 15 ato 15 h are supported by the respective supporting members 23 a to 23 huntil the downward movement of the core shaft 14 to be described belowis completed even after the split dies 15 a to 15 h are introduced intothe set ring 16.

After all of the split dies 15 a to 15 h are introduced into the setring 16, the first clamps 24 holding the compact W are horizontallymoved, and then the compact W is released from the first clamps 24 andis taken out from the disassembling-assembling machine 2 so that thestate is changed from the state shown in FIG. 10B to the state shown inFIG. 11A. Next, the core shaft 14 held by the second clamps 26 is moveddownward. Then, as shown in FIG. 11B, the lower end portion of the coreshaft 14 is inserted from above into the central portion of the splitdies 15 a to 15 h formed in a circular shape in the plan view, the innerperipheral surface of the set ring 16, and the inner peripheral surfaceof the cylindrical portion 21 a of the base 21, in the stated order.

After the core shaft 14 is inserted in this way, the lower surface ofthe protruding portion 14 b of the core shaft 14 abuts on the uppersurfaces of the respective split dies 15 a to 15 h, and presses thesplit dies 15 a to 15 h downward simultaneously. Consequently, the lowerend portion of the split dies 15 a to 15 h are introduced into andengaged with the engaging surface 16 b that is the tapered surface ofthe set ring 16. At this time, as the split dies 15 a to 15 h are moveddownward by the engaging surface 16 b, the split dies 15 a to 15 h aremoved toward the X axis and are engaged with the engaging surface 16 b.Therefore, the split dies 15 a to 15 h adjacent to each other in thecircumferential direction can be brought into close contact with eachother. Thus, the split dies 15 a to 15 h are in a circular shape in theplan view as a whole, and the inner die 12 is restored to its originalstate.

After the assembling of the inner die 12 is completed, the supportingmembers 23 a to 23 h are moved downward, and the split dies 15 a to 15 hare released from the respective supporting members 23 a to 23 h (referto FIG. 11B), and in addition, the set ring 16 is released from theholding members 22. Then, the lug portions 3 a of the chuck 3 are againengaged with the first engaging grooves 16 d of the set ring 16, theentire inner die 12 is raised, and the inner die 12 is returned to apredetermined position in the molding die 1 as shown in FIG. 3 (morespecifically, in the molding die 1 in a state where the compact W in thedrawing is removed). Then, from the state in which the inner die 12 isreturned to the predetermined position, the chuck 3 is disengaged, theejectors 18 are moved downward, and the inner die 12 is fitted in thefitting hole 13 b of the lower die 13 as shown in FIG. 1.

As described above, with the molding die for molding a boot for aconstant velocity joint in the present embodiment, the engaging surface16 b formed in the set ring 16 is the tapered surface whose diameter isgradually reduced downward. Therefore, when the upper end portions ofthe respective split dies 15 a to 15 h are pressed by the protrudingportion 14 b of the core shaft 14, the lower end portions of therespective split dies 15 a to 15 h are moved toward the X axis along theengaging surface 16 b and are engaged with the engaging surface 16 b.Thus, the split dies 15 a to 15 h adjacent to each other in thecircumferential direction can be brought into close contact with eachother. Accordingly, it is possible to prevent burrs from being generatedin the compact W molded by injection molding. Further, since theprotruding portion 14 b provided to protrude from the outer periphery ofthe upper end portion of the core shaft 14 serves as the pressingportion, the structure of the molding die 1 can be simplified, ascompared to a case where the pressing portion is provided as a bodyseparate from the core shaft 14.

By pulling the core shaft 14 downward using the pulling device 10, theprotruding portion 14 b of the core shaft 14 can be held in a statewhere the protruding portion 14 b is pressed against the split dies 15 ato 15 h. Therefore, the split dies 15 a to 15 h adjacent to each otherin the circumferential direction can be held in a state where the splitdies 15 a to 15 h are in close contact with each other. This caneffectively prevent burrs from being generated in the compact W moldedby injection molding. Further, since the lower end portions of therespective split dies 15 a to 15 h are brought into pressure contactwith the O ring 17 fitted to the set ring 16 when the split dies 15 a to15 h are introduced into the set ring 16, it is possible to restrain thesplit dies 15 a to 15 h from moving upward and downward with respect tothe set ring 16 from this state.

The invention is not limited to the above-described embodiment, and maybe realized in embodiments obtained by appropriately changing theabove-described embodiment. For example, the core shaft 14 in theabove-described embodiment is formed by the solid columnar member.However, the core shaft may be formed by a hollow cylindrical member.The pressing portion in the above-described embodiment is constituted bythe protruding portion 14 b provided to protrude from the core shaft 14.However, the pressing portion may be provided as a body separate fromthe core shaft 14. Further, although the core shaft 14 in theabove-described embodiment is inserted through and fitted to the setring 16 from above the set ring 16, the core shaft may be insertedthrough and fitted to the set ring 16 from below the set ring 16.

With the molding die for molding a boot for a constant velocity joint inthe invention, it is possible to prevent burrs from being generated inthe compact molded by injection molding.

What is claimed is:
 1. A molding die for molding a boot for a constantvelocity joint by injection molding, the molding die including an innerdie and an outer die arranged so that a cavity is formed between theinner die and the outer die, wherein the inner die includes a core shafthaving a circular outer peripheral surface and being arranged so that anaxis of the core shaft extends in an up-down direction, a plurality ofsplit dies radially arranged along the outer peripheral surface of thecore shaft around the axis of the core shaft, which serves as a center,and a cylindrical set ring arranged below the split dies, the core shaftbeing inserted through the set ring; wherein: an annular engagingsurface, which is a tapered surface whose diameter is gradually reduceddownward, is formed in an inner peripheral side of an upper end portionof the set ring, and lower end portions of the respective split dies areintroduced into, and engaged with the engaging surface; and the moldingdie includes a pressing portion that presses upper end portions of therespective split dies downward in a state where the lower end portionsof the respective split dies are introduced into the set ring, so as toengage the lower end portions of the respective split dies with theengaging surface and to bring the split dies into close contact witheach other.
 2. The molding die according to claim 1, wherein thepressing portion is constituted by a protruding portion that is providedto protrude from an outer periphery of the core shaft.
 3. The moldingdie according to claim 2, further comprising: a pulling device thatpulls a lower end portion of the core shaft downward so as to hold thepressing portion in a state where the pressing portion is pressedagainst the split dies.
 4. The molding die according to claim 3, whereinan opposed surface is formed in the lower end portion of each of thesplit dies, and the opposed surface faces an outer peripheral surface ofthe set ring in a state where the lower end portion of the split die isintroduced into the set ring, and wherein an O ring that is brought intopressure contact with the opposed surface is fitted to the outerperiphery of the set ring.
 5. The molding die according to claim 2,wherein an opposed surface is formed in the lower end portion of each ofthe split dies, and the opposed surface faces an outer peripheralsurface of the set ring in a state where the lower end portion of thesplit die is introduced into the set ring, and wherein an O ring that isbrought into pressure contact with the opposed surface is fitted to theouter periphery of the set ring.
 6. The molding die according to claim1, further comprising: a pulling device that pulls a lower end portionof the core shaft downward so as to hold the pressing portion in a statewhere the pressing portion is pressed against the split dies.
 7. Themolding die according to claim 6, wherein an opposed surface is formedin the lower end portion of each of the split dies, and the opposedsurface faces an outer peripheral surface of the set ring in a statewhere the lower end portion of the split die is introduced into the setring, and wherein an O ring that is brought into pressure contact withthe opposed surface is fitted to the outer periphery of the set ring. 8.The molding die according to claim 1, wherein an opposed surface isformed in the lower end portion of each of the split dies, and theopposed surface faces an outer peripheral surface of the set ring in astate where the lower end portion of the split die is introduced intothe set ring, and wherein an O ring that is brought into pressurecontact with the opposed surface is fitted to the outer periphery of theset ring.